As an image reading apparatus connected to an external apparatus such as a computer or the like when it is used, an image reading apparatus, which operates using electric power supplied from a power supply of the external apparatus via a connection cable such as a USB cable or the like, or using electric power supplied from an AC power supply, is known.
When such image reading apparatus operates using electric power supplied from a power supply of an external apparatus, it may often fail to operate normally due to insufficient electric power. This problem is posed when electric power supplied from the external apparatus via the connection cable is smaller than peak electric power that the image reading apparatus requires. Thus problem readily occurs when the external apparatus is driven using a battery. This is because the battery equipped in the external apparatus normally guarantees the operation of only the external apparatus itself.